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The potential climate-warming impact from aircraft contrails may be similar in magnitude to the direct effect from carbon dioxide emissions across all aviation. The warming impact may be mitigated through pre-tactical flight trajectory optimization to avoid ice supersaturation regions (ISSRs) while also considering aircraft performance and CO 2 emissions. The ability to perform such deviations depends on accurate predictions of water vapor in the upper troposphere and lower stratosphere (UTLS). Herein we evaluated the performance of two leading global numerical weather prediction (NWP) models: the Global Forecast System (GFS) developed in the USA and the Integrated Forecast System, (IFS) developed in Europe, and a research mesoscale model, Weather Research and Forecasting configured by SATAVIA (S-WRF) to predict UTLS moisture and ISSR. We compared humidity forecasts to observations from 383 aircraft flights and 3480 radiosonde profiles comprising approximately 1.5 million measurements over Europe and the Middle East for 10 months in 2022. Neither GFS nor IFS properly reproduced the observed distribution of relative humidity with respect to ice (RH ice). Moreover, in addition to not being usable for prospective flight planning, the ERA5 reanalysis only slightly improved the outcome of the IFS. Only the S-WRF model with multi-moment cloud physics and high spatial resolution (5 km grid spacing) closely reproduced the observed relative frequency distribution of RH ice. Furthermore, ISSR validation using near equal-area neighborhoods when computing Matthews Correlation Coefficient and F1 score showed that S-WRF scored higher (F1 = 0.66) than the IFS (F1 = 0.62), while the GFS had near zero score due to its near complete lack of predictions of RH ice greater than 100 % in stark contrast to observations. In fact, S-WRF also correctly predicts 92 % of the time when conditions were not conducive to contrail formation. Ultimately, the S-WRF model could be used to alter flight plans to deviate above or below nearly certain contrail formation regions to reduce non-CO 2 climate impacts of aviation. • Statistical analysis of upper-tropospheric, lower-stratospheric moisture predictions. • Skill of forecasts of relative humidity with respect to ice. • Numerical weather prediction of ice supersaturation and contrail formation regions. • Applicability of numerical weather prediction of contrails to re-route aircraft in order to prevent contrails. • Reducing non carbon dioxide impacts of aviation by contrail management. [ABSTRACT FROM AUTHOR]

The continuous rise in greenhouse gases (GHGs) in the atmosphere is one of the major factors responsible for the global warming and enhanced tropospheric temperature. In this context, we examine the long-term spatiotemporal changes in the tropospheric temperature (1000–100 hPa) in India using radiosonde measurements and the reanalysis data from European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5), Modern-Era Retrospective analysis for Research and Application Version 2 (MERRA2) and National Center for Environmental Prediction (NCEP) for the period 1980–2020. We also investigate the future projections of tropospheric temperature in the Shared Socio-economic Pathways (SSPs) 2–4.5 and 5–8.5 by using the Coupled Model Intercomparison Project 6 (CMIP6) results for the period 2015–2100 over India. Our analysis shows a significant positive trend (0.01–0.04 °C/yr) in the annual mean temperature in the upper troposphere (500–100 hPa) in India during the period 1980–2020. The warming trends are also noticeable in the middle and lower troposphere of India. Among the regions, the northeast, north central and northwest India exhibit significant warming of about 0.01–0.06 °C/yr in the upper troposphere (500–100 hPa). On the other hand, most regions show a decline in temperature at the tropopause (100 hPa), which is stronger in the interior peninsular, north central and east coast of India, at about −0.05 ± 0.01 °C/ yr. All reanalysis data show consistent warming and cooling trends in the respective regions as observed from the radiosondes, albeit slight differences in their values. The future high emission scenario of SSP5–8.5 shows a warming trend of about 0.04–0.08 °C/yr at 1000–200 hPa by the end of the century, which is highest at 250 hPa. The increasing trend in tropospheric temperature is a serious concern, which calls for adaptation and mitigation measures to alleviate the impacts of this accelerated warming in India. [Display omitted] • Tropospheric warming of 0.01–0.04 °C/yr is found in India during 1980–2020. • Northeast India shows high trends of about 0.024 ± 0.01 °C/yr at 700 hPa. • Northwest India shows a trend of 0.03 ± 0.014 °C/yr at both 500 and 700 hPa. • The SSP5–8.5 scenario shows a high warming of 0.04–0.08 °C/yr in 2015–2100. [ABSTRACT FROM AUTHOR]

The lack of reliable and continuous measurements of the atmospheric boundary layer (ABL) height poses a significant problem for accurate weather forecasting and examining the intricate dynamics between the ABL and the free troposphere (FT). To address this crucial scientific problem, the present study investigates the ABL height from various simultaneous observations of multi-remote sensing instruments Micropulse lidar (MPL), Ceilometer (CL), Wind profiler radar (WPR) and Radiosonde (RS) and four different PBL schemes (Asymmetrical Convective Model version 2 (ACM2), Yonsei University (YSU), Mellor-Yamada Nakanishi and Nino level 2.5 (MYNN2), and Bougeault–Lacarrere (BouLac) during different sky and surface conditions. The diurnal variation of ABL heights between observation and model differs by ∼230 m. The ACM2 and MYNN2 show better performance (R > 0.85) of ABL height than other numerical schemes. The ABL height from different observations such as CL, WPR, MPL, RS and simulated ACM2 and MYNN2 is about 1098 ± 196 m, 1303 ± 217 m, 1461 ± 391 m, and 1716 ± 639 m, 1808 ± 407 m, and 1585 ± 393 m respectively, during the radiosonde launching time (∼11:00–12:00 IST). The difference in mean ABL height is observed due to their different measurement techniques and tracer identity between observation and model simulations. The study underscores a consistent and abrupt reduction in ABL height between observations (<480 m), model simulations (∼700 m), and re-analysis data sets (∼550 m) during wet-surface conditions, highlighting the model's ability to replicate consistent ABL behaviour in different surface conditions. While in cloudy conditions, the WRF-model underestimates ∼50–200 m than the observed ABL. This discrepancy is mainly observed due to the underestimation of sensible heat flux and downward shortwave radiation in model simulations. Due to the distinct ABL growth rate difference between the model (∼100–200 m/h) and observations (∼105–130 m/h), the time of attaining peak ABL height differs by one hour among them during different sky conditions. This is attributed to the large deviation in surface temperature, the incoming solar radiation, and the sensible heat fluxes. • This study explores ABL height from observations and four different PBL schemes during different sky and surface conditions. • The ACM2 and MYNN2 shows the better performance of ABL height than other numerical schemes. • SHF and downward SWR in model simulations leads differences in the ABL against observations in different conditions. • Slower growth rate of ABL during cloudy conditions delays reaching the peak ABL height by one hour than clear-sky. [ABSTRACT FROM AUTHOR]

The weighted mean temperature (Tm) is an essential parameter in the field of Global Navigation Satellite System (GNSS) meteorology, as it enables the conversion of zenith wet delay to atmospheric precipitable water vapor (PWV). The existing Tm models, such as the GPT3 model, utilize the empirical annual and semi-annual amplitudes of Tm at grid points along with corresponding trigonometric functions to estimate Tm, making it difficult to provide a more detailed description of the daily variation of Tm. Therefore, the measured surface temperature and water vapor pressure were introduced to calculate the new series of grid coefficients using the least-square method, which enables the GPT3 model to estimate Tm with higher accuracy. In this process, the ERA5 reanalysis data derived from ECMWF from 2001 to 2010 was utilized to compute Tm values, and the new grid coefficient obtained by introducing only surface temperature was considered as scheme #1 and that achieved by introducing both surface temperature and surface water vapor pressure was regarded as scheme #2. The Tm data of 2023 calculated both by the radiosonde and ERA5 reanalysis data were utilized to assess the new grid coefficients for Tm estimation, and the results show that the grid coefficients based on these two surface parameters outperformed those only using the temperature. In the compassion using the ERA5 data, the bias/MAE/RMSE with the two types of new grid coefficients are −0.09/1.89/2.41 K and − 0.07/1.82/2.31 K, respectively, and the improvements reach to 50%/32.5%/34.2% and 61.1%/35%/36.9% compared with GPT3 model. In the comparison with radiosonde data, the scheme #1 and #2 performed a 0.55 K(13.8%) and 0.68 K(17.1%) improvement in the mean RMSE of stations compared with the GPT3 model. Note that the proposed two schemes can effectively improve the accuracy of estimating Tm in the comparison of regions, epochs and seasons with the Bevis and GPT3 model. Furthermore, the impact of Tm on PWV can be improved by the proposed two schemes, which was demonstrated using the theoretical RMSE and relative error of PWV. • A refined method for weighted mean temperature using GPT3 with new grid coefficients was proposed. • Two types of new grid coefficients were achieved using the measured surface temperature and water vapor pressure. • The proposed schemes were validated using the ERA5 and radiosonde data in China to obtain Tm with higher accuracy. [ABSTRACT FROM AUTHOR]

The Index of Coalescence Activity (ICA) is an indicator of the microphysical state of the cloud. ICA is related to cloud base temperature and buoyancy of cloud at 500 hPa level. It is a useful parameter for making a decision on the type of seeding to be carried out. During Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) over the Indian region, aircraft operations for in situ measurements of aerosols and clouds were conducted from the base station Hyderabad to cover parts of north peninsular India falling under the rain-shadow region. Special Radiosonde flights were conducted in the afternoon hours prior to aircraft operations from the locations Hyderabad and Mahabubnagar in addition to regular India Meteorological Department (IMD) Radiosonde flights at 00 UTC from Hyderabad. The parameters like cloud base height and buoyancy at 500 hPa level obtained from Radiosonde flights have been used to estimate ICA values during the period of the experiment (June to October 2009–2011). The variability of ICA has been studied using morning and afternoon sounding profiles over the rain-shadow region. Morning hours showed highly negative ICA values, as compared to noon hours. During noon time, positive ICA values are observed before monsoon onset (in 2009, monsoon onset was 21st June over the study area) and on few occasions during post-monsoon (October). Positive ICA values represent that collision-coalescence (CC) process is not fully developed and hence, hygroscopic seeding is the proper decision. While, negative ICA values indicate active CC process, suggesting glaciogenic seeding. The soundings conducted just before the cloud seeding operations provide information about the actual thermodynamic and microphysical state of the cloud. Hence, ICA information is useful for providing guidelines to the operational cloud seeding programs. • Variability of ICA is investigated over a rain-shadow region in peninsular India. • Negative ICA during monsoon represent glaciogenic seeding to trigger rainfall. • Positive ICA in pre-monsoon/weak monsoon represent hygroscopic seeding. • ICA reveals change in microphysical state of the cloud after monsoon establishment. • ICA an important indicator for making cloud seeding decisions. [ABSTRACT FROM AUTHOR]

Climatology of atmospheric instability is studied over Gadanki using high-resolution radiosonde launched daily during April 2006 to April 2017. The diurnal and seasonal variation of instability parameters is discussed in relation with surface meteorological parameters. Seasonal variations depict strong variability in instability which is masked by stronger diurnal variation with descending Lifting Condensation Level (LCL) and Level of Free Convection (LFC) between 11 and 18 IST resulting in high Convective Available Potential Energy (CAPE) values and heavy rainfall. On a seasonal basis, parcel parameters are high during the late monsoon and post-monsoon while the instability parameters like Total Totals index (TT) and Vertical Totals index (VT) show highest values in the pre-monsoon associated with strong convection. LFC and LCL start descending with ascent in Equilibrium Level (EL) before the monsoon onset. However after the onset, atmospheric instability falls sharply as supported by decreasing TT, VT and CAPE with increasing LI. The 11-year long-term variation depicts slightly elevated LFC and LCL and declining EL values indicating a decrease in the instability with a decrease in CAPE and K Index (KI) and increase in Lifted Index (LI) and Convective Inhibition (CIN). [ABSTRACT FROM AUTHOR]

Water vapor is one of the major greenhouse gases in the atmosphere and also the key parameter affecting the hydrological cycle, aerosol properties, aerosol-cloud interactions, the energy budget, and the climate. This study analyzed the temporal and spatial distribution of precipitable water vapor (PWV) in China using MODerate resolution Imaging Spectroradiometer near-infrared (MODIS-NIR)-Clear PWV products from 2011 to 2013. We then compared the four PWV products (Global Positioning System PWV (GPS-PWV), radiosonde PWV (RS-PWV), MODIS-NIR-Clear PWV, and Aerosol Robotic Network sunphotometer PWV (AERONET-PWV)) at six typical sites in China from 2011 to 2013. The analysis of the temporal and spatial distribution showed that the PWV distribution in China has clear geographical differences, and its basic distribution characteristics gradually change from the coast in the southeast to inland in the northwest. Affected by the East Asian monsoon, the PWV over China showed clear seasonal distribution features, with highest values in the summer, followed by autumn and spring, and the lowest values in winter. Intercomparison results showed that GPS-PWV and RS-PWV had a slightly higher correlation (R 2 = 0.975) at 0000 UTC than that at 1200 UTC (R 2 = 0.967). The mean values of Bias, SD, and RMSE between GPS-PWV and RS-PWV (GPS-RS) were − 0.03 mm, 2.36 mm, and 2.60 mm at 0000 UTC, and − 0.23 mm, 2.76 mm, and 2.95 mm at 1200 UTC, respectively. This showed that GPS-PWV was slightly lower than RS-PWV, and this difference was more obvious during the nighttime. The MODIS-NIR-Clear PWV product showed a similar correlation coefficient (R 2 = 0.88) with GPS-PWV compared with RS-PWV. In addition, MODIS-NIR-Clear PWV was greater than GPS-PWV and RS-PWV. The MODIS-NIR-Clear PWV showed a larger deviation from GPS-PWV (MODIS-GPS Bias = 1.50 mm, RMSE = 5.76 mm) compared with RS PWV (MODIS-RS Bias = 0.75 mm, RMSE = 5.31 mm). The correlation coefficients between AERONET-PWV and the PWV from GPS, RS, and MODIS-NIR-Clear were 0.970, 0.963, and 0.923 (with RMSE of 2.53 mm, 3.67 mm, and 4.39 mm), respectively. In the Beijing area, the overall mean bias of the AERONET-PWV product with GPS-PWV, RS-PWV and MODIS-NIR-Clear PWV was − 0.09 mm, − 1.82 mm, and − 1.54 mm, respectively, which shows that the AERONET-PWV product was lower than the other three PWV products. [ABSTRACT FROM AUTHOR]

The thermodynamic structure of the atmospheric boundary layer for contrasting sky conditions over Chennai, a coastal station in the Indian subcontinent, is investigated through conserved variable analysis of equivalent potential temperature and specific humidity. Simultaneous radiosonde and micropulse lidar measurements undertaken in 2018 constitute the primary database in this investigation. One of the most prominent features of this analysis is a consistent occurrence of a double mixed layer structure during the clear-sky and cloudy conditions throughout the year. The occurrence frequency of the double mixing lines is higher during the pre-monsoon season compared with the winter and northeast (NE) monsoon seasons. The advection mainly dominates the formation of double mixing lines during the winter and pre-monsoon seasons. In contrast, convection and advection dominate during the southwest (SW) and NE monsoon seasons. The frequent double mixing lines over Chennai occur mainly from the restratification of the convective boundary layer (CBL) due to the sea-breeze onset and the cloud layer. Occasionally, a triple mixing line structure is also observed during the fair-weather boundary layer (FWBL) of the pre-monsoon and SW monsoon seasons. Among the 355 total observations collected during 2018, the first, second, and third mixing lines occurred 100%, 70%, and 14%, respectively. The thermal internal boundary layer (TIBL), CBL, and FWBL occur ∼50%, ∼97%, and ∼ 30%, respectively. The first mixing line is represented by both the TIBL and CBL, and CBL and FWBL represent the second mixing line, whereas the third mixing line is represented solely by the FWBL. The first and second mixing line shows strong seasonal variations with lower altitudes during the pre-monsoon season and higher altitudes in the SW monsoon season, almost in the same phase as the CBL variation but in the opposite phase of the TIBL variations. The CBL height attains a minimum during the winter season and maximum during the SW monsoon season, while TIBL becomes minimum during the pre-monsoon and SW monsoon seasons and maximum during winter and NE monsoon seasons. Figure: (a) The locations of the observation sites of MPL over Kattankulathur (12.82oN, 80.04°E, 45 m a.m.s.l), radiosonde and AWS datasets from IMD Chennai at Meenambakkam (13.0oN, 80.18°E, 16 m a.m.s.l). Typical profiles of temperature (θ v , θ e , θ es), water vapor mixing ratio (q), and saturation pressure deficit (P), time-height section of the normalized backscatter (NRB) coefficient superimposed with θ profile, diagram of conserved variable analysis using θ e and q, profiles of the advection and convection components observed during (b) clear sky condition on 27 January 2018, and (c) cloudy condition on 20 September 2018. [Display omitted] • Thermodynamic structure of the boundary layer using simultaneous radiosonde and micropulse lidar observations. • Demonstration of the double and triple mixing lines and their association with convection and advection. • The first mixing line is the true representation of the boundary layer over the coastal station. • The first mixing line is associated with advection, and the convective boundary layer is with both convection and advection. • Thermodynamic features of the atmospheric boundary layer are vital in understanding its coupling with the free troposphere. [ABSTRACT FROM AUTHOR]

Combination of radiosonde profiles with collocated in-situ ground and aircraft measurements is used for the first time to study the vertical structure and microphysics of clouds during southwest monsoon over the Western Ghats, India. The morphology of clouds is detailed with the help of radiosonde observations and classified as low, mid, and high-level clouds depending on the cloud base height. Radiosonde sounding profiles indicated occurrences of both single and multi-layered clouds with higher occurrences of single-layered (∼35%) clouds during monsoon transition period (June and September) and two-layered (∼42%) during core monsoon period (July and August). Dominance of low (∼30%) and high-level (∼60%) clouds were noticed compared to mid-level clouds over the observational site during the southwest monsoon. Warm cloud microphysics was investigated using collocated ground and airborne in situ measurements. Irrespective of the cloud type, the cloud liquid water content and the effective droplet diameter increased with altitude. One of the key results is the rapid broadening of the cloud droplet size distribution with height. The number concentration of droplets above 25 μm diameters showed a steep decrease at altitudes above 1800 m, suggesting active collision-coalescence. • Collocated observations of the vertical structure and microphysics of clouds over Western Ghats, India. • Cloud morphology is detailed using radiosonde observations over WG. • Warm cloud microphysics is investigated using collocated in-situ ground and airborne cloud measurements. • Rapid broadening of the cloud droplet size distribution with height was noticed. • This is the first such report over a complex terrain like Western Ghats in India. [ABSTRACT FROM AUTHOR]

Global Navigation Satellite Systems (GNSS) water vapor tomography has been proved to be an effective method for retrieving three-dimensional (3D) water vapor distribution. Currently, due to the limitation on the availability and the poor distribution of observations, the ill-posed problem of the tomographic system still needs to be solved. In this study, a refined extended tomographic model with combining virtual signals is proposed to address the observational geometry defect and improve the performance of tomographic solutions. The new refined model was generated by adding auxiliary voxels of the same size as the original voxels around the original tomographic model and its tomographic body is with an inverted cone shape. Then, "virtual" signals that pass through the sides of the original tomographic body and the top boundary of the extended region are introduced. The slant wet delays (SWDs) of these virtual rays were obtained from the tropospheric parameters estimated from GNSS data processing and pre-defined elevation and azimuth angles. Three experimental schemes based on GNSS data from the Hong Kong reference network during the 30-day period in July 2019 were implemented to evaluate the proposed tomographic model. Statistical results showed that, compared with the tomographic models of other schemes, the new model shows strong robustness in terms of observational geometry and the accuracy of the 3D water vapor field inferred. The mean value of the root-mean-square errors (RMSEs) of the tomographic solutions during the period studied obtained from the proposed method was improved by 12% and 11% compared with Schemes I and II, when radiosonde data were used as the reference. Furthermore, compared to other schemes, the condition number of the design matrix reduced after the side-crossing virtual signals were added, implying improvements in the ill-condition of a tomographic system for the proposed method. All these results suggest the good performance of the proposed method. • An improved tomographic model is proposed to address the observational geometry defect and improve the performance. • The virtual signals penetrating from the side-faces of the tomographic model are incorporated into the observation eqs. • The new model with an inverted cone shape is built to utilize these virtual signals. [ABSTRACT FROM AUTHOR]

Precipitable Water Vapor (PWV) and rainfall play important roles in the meteorological processes. In this study, we have investigated the impact of assimilation of Global Navigation Satellite System (GNSS) PWV and radiosonde profiles on the performance of Weather Research and Forecasting (WRF) model in forecasting PWV and rainfall over the South China region for April 01, 2020 to May 31, 2020. PWV observations derived from 213 GNSS stations and meteorological profiles recorded by 23 radiosonde stations are assimilated into WRF model. Five different WRF schemes are adopted: WRF scheme 0: no data assimilation (DA); WRF scheme 1: assimilation of PWV from 76 GNSS stations; WRF scheme 2: assimilation of PWV from 213 GNSS stations; WRF scheme 3: assimilation of meteorological profiles from 23 radiosonde stations; WRF scheme 4: assimilation of both PWV from 213 GNSS stations and meteorological profiles from 23 radiosonde stations. PWV observations derived from 170 independent GNSS (have not been used in assimilation) and rainfall data recorded by 648 surface meteorological stations are used to evaluate WRF forecasting performance in PWV and rainfall, respectively. The results indicate that all DA schemes improve the WRF forecasting performance for both PWV and rainfall. For the first 6 h after data assimilation, WRF schemes 1 to 4 improve the PWV forecasting accuracy by 11.6%, 14.5%, 2.9%, and 14.8%, respectively. For the accumulated rainfall within the first 6 h after data assimilation, WRF scheme 2 and WRF scheme 4 have a similar performance and outperform other DA schemes while the WRF scheme 4 is the best one among all five schemes. WRF scheme 4 improves the rainfall forecast probability of detection and equitable threat score by 0.085 and 0.057, respectively. • Impact of assimilation of GNSS PWV and radiosonde profiles over the South China are investigated; • The first 6-h WRF PWV forecasting accuracy is improved by 14.8% after data assimilation; • The first 6-h accumulated rainfall forecast scores are improved by 0.085 after data assimilation. [ABSTRACT FROM AUTHOR]

Microwave radiometer is an effective instrument to monitor the atmosphere continuously in different weather conditions. It measures brightness temperatures at different frequency bands which are subjected to standard retrieval methods to obtain real time profiles of various atmospheric parameters such as temperature and humidity. But the retrieval techniques used by radiometer have to be adaptive to changing weather condition and location. In the present study, three retrieval techniques have been used to obtain the temperature and relative humidity profiles from brightness temperatures, namely; piecewise linear regression, feed forward neural network and neural back propagation network. The simulated results are compared with radiosonde observations using correlation analysis and error distribution. The analysis reveals that neural network with back propagation is the most accurate technique amongst the three retrieval methods utilized in this study. [ABSTRACT FROM AUTHOR]

Diurnal variability of atmospheric stability as well as the occurrence and strength of turbulence in the troposphere and lower stratosphere at two tropical stations, Trivandrum (8.5°N, 76.9°E) and Gadanki (13.5°N, 79.2°E), situated in the Indian Peninsula is studied. For the analysis three years of GPS-radiosonde data, collected as a part of the Tropical Tropopause Dynamics (TTD) Experiment under the CAWSES-India program, has been used. Thorpe method is adopted to estimate the turbulent parameters from radiosonde observations. This study shows that in the atmospheric boundary layer, both stability and turbulence parameters depict a pronounced diurnal variation. Over Trivandrum, the occurrence of turbulence as well as its strength peaks during night and falls off during the day, while at Gadanki it shows an opposite pattern. At both the stations, in the 3–10 km altitude layer, the occurrence and strength of turbulence are relatively high during night compared to day. Although the turbulence strength in the 10–15 km altitude layer is rather weak at both the stations, the occurrence of turbulence shows a clear diurnal pattern (high during the day), especially over Trivandrum. In the 3–15 km altitude layer, while the occurrence of convective instability is fairly the same at both the stations, the wind shear is significantly large at Trivandrum compared to Gadanki, with high values during night compared to the day. This shows that in this altitude region, while convective instability is mainly responsible for the generation of turbulence at Gadanki, wind shear induced dynamic instability is also responsible for the generation of turbulence at Trivandrum especially during night. Above 15 km, where wind shear driven instability leads the convective instability, turbulence at both the stations does not show any significant diurnal variability. [ABSTRACT FROM AUTHOR]

Clouds substantially affect Earth's energy budget by their interactions with short/long-wave radiation, and small changes in cloud vertical structure (CVS, i.e., the locations of cloud base and top, the thickness and number of cloud layers) can fluctuate the warming effects of anthropogenic forcing. However, the knowledge regarding how the CVS changes over time is still poor owing to a lack of reliable and available datasets. Here, the long-term temporal variations in four-times-daily radiosonde-derived CVS at Lindenberg, Germany, from 1992 to 2020 are analyzed. Robust increasing trends in cloud height/thickness and overlap frequency are found during this three-decade period. Observational results show that the interannual variabilities of the cloud-top height, cloud-base height, and cloud thickness are consistently increasing, with linear trends of 137.75 ± 6.65 m yr−1, 45.73 ± 6.22 m yr−1, and 29.52 ± 3.53 m yr−1, respectively. The occurrence of multi-layer cloud generally increases with a trend of 1.57 ± 0.06% yr−1, whereas the percentages of single-layer cloud and cloudless conditions decrease with trends of −0.44 ± 0.05% yr−1 and −1.12 ± 0.07% yr−1, respectively. Continuous surface warming increases thermal instability, which raises cloud height, particularly for single-layer clouds and the lower layer of multi-layer clouds. The upper-level cloud generates and maintains itself as the upper water vapor and vertical velocity enlarge, thus increasing the cloud top height, total cloud thickness, and cloud overlap frequency. These findings shed new light on the long-term changes in cloud properties caused by climate change. • Long-term (1992–2020) trends inCVS at Lindenberg, Germany, are examined using updated radiosonde data. • Robust increasing trends in cloud height/thickness and overlap frequency are observed, which is driven by climate change. • The influences of thermodynamic, dynamic, and moisture factors on the CVS trends are analyzed and explained. [ABSTRACT FROM AUTHOR]

In the present study, the effectiveness of nowcasting convective activities using a microwave radiometer has been examined for Kolkata (22.65° N, 88.45° E), a tropical location. It has been found that the standard deviation of brightness temperature (BT) at 22 GHz and instability indices like Lifting Index (LI), K Index (KI) and Humidity Index (HI) has shown definite changes before convective events. It is also seen that combination of standard deviation of BT at 22 GHz and LI can be most effective in predicting convection. A nowcasting algorithm is prepared using 18 isolated convective events of 2011 and in all cases, a marked variation of these parameters has been seen an hour before the event. Accordingly, a prediction model is developed and tested on convective events of 2012 and 2013. It is seen that the model gives reasonable success in predicting convective rain about 7075 min in advance with a prediction efficiency of 80%. [ABSTRACT FROM AUTHOR]

The role of deep convection on the tropical tropopause parameters at sub-daily scales using radiosonde observations at two locations in South-India affected by monsoon has been investigated. Special experiments were conducted under the Tropical Tropopause Dynamics (TTD) campaigns from two stations, (Gadanki (13.5°N, 79.2°E) and Trivandrum (8.5°N, 76.9°E) as a part of CAWSES India Phase-II programme during December 2010 to September 2013. In addition, data from regular radiosonde launches available from April 2006 to September 2013 are also utilized in the present study. Using satellite based infrared brightness temperature data, convection is classified into six categories based on the life cycle of the convection prevailing 3 h before and after the balloon reaching the tropical tropopause. Cold-point and lapse rate tropopause altitudes (CPH, LRH) and temperatures (CPT, LRT), convective outflow level (COH) and tropical tropopause layer (TTL) thickness extracted from individual soundings are grouped into six convection categories. Large amount of water vapour with diabatic cooling prevailed near the CPH during active convection leading to STE processes. At the same time, decrease in TTL thickness is observed not only because of pushing up of the COH but also due to decrease of CPH. On an annual basis a decrease (increase) in CPH and LRH (CPT and LRT) is noticed during active convection. This feature is more significant at Gadanki compared to Trivandrum. During the monsoon and pre-monsoon periods when the convection is rather widespread, CPH (CPT) shows a decrease (increase) at Gadanki while it increases (decreases) over Trivandrum. Large seasonal variation is noticed in the tropopause parameters even when they are segregated into different convective categories mainly due to intensity of the convection being different. During active convection, diabatic and adiabatic processes seem to be dominant at Gadanki and Trivandrum, respectively. [ABSTRACT FROM AUTHOR]

Abstract: This study is mainly devoted to operational meteorology, to improve tornado forecast in Poland and create a Universal Tornadic Index formula. A study is focusing on climatology of sounding-derived parameters associated with tornadoes in Poland and their potential value for tornado forecasting. The data was collected from soundings made in 10 stations in and around Poland which were closely in time and space connected with tornado occurrence. The main aim of the study was to analyze the thermodynamic and kinematic parameters derived from soundings and formulate an index. The information about tornado incidents was taken from media reports and the European Severe Weather Database for the years 1977–2012. Total of 97 tornado cases were divided according to their strength for significant (F2/F3), weak (F0/F1) and unrated cases, and also according to their environmental surface temperature, for warm (>18°C) and cold (<18°C) tornadoes. As it turned out, depending on the temperature, tornadoes tended to present different environmental conditions for tornadogenesis. In warm cases, the most important factor was instability while for cold cases it was dynamic wind field. It was also proven that significant tornadoes in Poland occur in conditions accompanied by high moisture content, moderate instability and high wind shear conditions. The results of this study were used to create a Universal Tornadic Index designed to forecast activity in warm and cold, and weak and strong tornadic environments. The quality of this index was tested for the period with increased tornado activity in Poland from 2008 to 2010. [Copyright &y& Elsevier]

Abstract: The strong southwesterly and northeasterly flow in the lower troposphere during June–September (southwest, SW) and October–December (northeast, NE) monsoons bring substantial moisture into Indian sector. In this observational study, moisture variability over Hyderabad which is completely influenced by SW monsoon, Chennai influenced by NE monsoon and Gadanki influenced mostly by NE monsoon and partly by SW monsoon is studied. For the first time we have characterized the vertical variations in moisture based on background wind shear. The moisture variability over Indian monsoon region is compared with western Pacific and found that moisture variations are similar to western Pacific except during monsoon season. The correlation between the total precipitable water and water vapor mixing ratio is found maximum in boundary layer (BL) and decreases in free atmosphere. In general, the total precipitable water between the 850 and 600hPa is found higher than between 900 and 850hPa. To investigate the origin of air masses, back trajectories were calculated with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and found that wet events are originated from lower altitudes and from the Bay of Bengal. The moisture variability is found the same during both wet and dry spells within the BL but differ significantly in the mid-troposphere suggesting that the moisture above the BL plays significant role in maintaining the precipitation conditions over Indian region. [Copyright &y& Elsevier]

Abstract: Convection plays an important role in maintaining the thermodynamic structure of the atmosphere particularly in the tropical regions and it is often associated with clouds and precipitation. In the present study we report the diurnal variation of various stability indices observed using intensive radiosonde observations made during October 2010 to October 2011 over Indian tropical region, Gadanki (13.5°N, 79.2°E). Simultaneous co-located microwave radiometer (MWR) observations collected during April–October 2011 are used for comparison. Detailed comparison between these two independent techniques has been made which will be very much useful in assessing the data from MWR for Nowcasting. In general, MWR observations show warm (cold) bias in the temperature, except at 0.5km, when compared to radiosonde observations below (above) 3–4km, assuming latter as a standard technique. In case of water vapor, MWR observations show wet (dry) bias below (above) 2–3km depending on the time. Nevertheless, very good comparison in several convection indices is noticed between the two different techniques, particularly in the trends though some differences are noticed in the amplitudes. For about 25% of time MWR is unable to estimate the Convective Available Potential Energy (CAPE) as equilibrium level is above the altitude that MWR can detect. Strong diurnal variation in CAPE and other thermodynamic parameters is noticed with maximum in the afternoon and minimum in the early morning hours in all the seasons except in winter over this tropical station. [Copyright &y& Elsevier]

Abstract: Atmospheric water vapour is an essential component of the terrestrial atmosphere and must be known precisely in a wide range of applications such as radiative transfer modelling or weather forecasting to mention just a few examples. Vertically integrated measurements, or total precipitable water (TPW) equivalent amounts traditionally derived from radiosonde measurements, are needed in many of these applications and can also be obtained from other methodologies such as sunphotometers or GPS-based techniques. This paper presents a study comparing different measurements of TPW from radiosonde and sunphotometer data recorded from 2001 to 2004 in Barcelona, Spain. Three collocated instruments were employed in this study: RS-80A Vaisala sondes and two types of commonly used sunphotometers (Cimel 318N-VBS7 and Microtops II). A cloud screening filter was applied to photometer data based on the quality control procedure of the AERONET database. A systematic comparison among the measurements indicates that bivariate correlations between different instruments were high, with correlation factors (r 2) above 0.8 in all cases. Measurements covered all seasons allowing examining intra-annual variability, which generally did not exhibit statistically significant differences. Examination of 57 concurrent measurements of the three instruments indicated that radiosonde TPW measurements were the highest (15mm on average) and Cimel and Microtops presented similar values (12mm and 11mm respectively). [Copyright &y& Elsevier]

Temperature inversion (TI) has long been recognized to play an important role in air quality and convection initiation, mainly through modulating the dynamic and thermodynamic processes of planetary boundary layer (PBL). Yet, our knowledge remains poor regarding the relationship between TI and the synoptic systems. Here we use nine years (2011–2019) of high-resolution radiosonde data from the Beijing site to quantify the impact of TI on the dynamic and thermodynamic conditions associated with the activities of synoptic systems. The monthly, seasonal and diurnal changes of the TI occurrence frequencies are first analyzed, and the surface-based inversions (SBIs) are found more related to the surface properties, whereas elevated inversions (EIs) are potentially more influenced by thermodynamic and dynamic characteristics of the atmosphere. A novel method based on the threshold of seasonal averaged sea level pressure for identifying the centers of high-pressure system (HPS) and low-pressure system (LPS) is developed. Statistical analyses show that the pressure gradients are stronger in the presence of TI, when HPS or LPS centers approach the observational site of interest from the northwest. The pressure difference becomes larger between the center and the site when the HPS or LPS center locates farther. Height-resolved zonal and meridional temperature advection and wind anomalies are further investigated, showing that the EIs are possibly related to the downslope intrusion of cold air under the control of HPS and to the heat transportation under the control of LPS over the mountain slopes. The TI-favored temperature advection brought by the prevailing wind of the synoptic systems, aided by topographic uplifting, may also reinforce the occurrence of EI. • Impact of synoptic system is analyzed on temperature inversion (TI) as obtained from radiosonde data in Beijing for the period 2011–2019. • A novel method is developed to determine high- and low-pressure center, whose location and strength are closely linked to TI occurrence. • Temperature advections brought by synoptic systems together with the topographic uplift facilitate the formation of TIs. [ABSTRACT FROM AUTHOR]

The amplification of global warming because of the feedbacks associated with the increase in atmospheric moisture and the decrease in sea ice and snow cover in the Arctic is currently the focus of scientists, policy makers and society. The amplification of global warming is the response to increases in precipitation originally caused by climate change. Arctic predominant increases in specific humidity and precipitation have been documented by observations. In comparison, evapotranspiration in the Arctic is poorly known, in part, because the spatial and temporal sparsity of accurate in situ and remote sensing observations. Although more than 20 observations sites in the Arctic are available, where AERONET sun photometer integrated water vapor (IWV) measurements have been conducted, that information have been barely used. Here, we present a comparison of IWV observations from radiosondes and AERONET sun photometers at ten sites located across the Arctic with the goal to document the feasibility of that set of observations to contribute to the ongoing and future research on polar regions. Sun photometer IWV observations are averaged for three-time windows; 30 min, 6 and 24 h. The predominant dry bias of AERONET IWV observations with respect to radiosondes, identified at tropical and midlatitudes, is also present in the Arctic. The statistics of the comparison show robust results at eight of the ten sites, with precision and accuracy magnitudes below 8 and 2% respectively. The possible causes of the less robust results at the other two sites are discussed. In addition, the impact of selecting other temporal coincidence windows in the average sun photometer IWV used in the comparison were tested. Auto-correlation in diurnal sun photometer IWV could produce appreciable bias in the statistics used for the comparison. We suggest using only one pair of values per day, consisting in the daily mean IWV sun photometer and the IWV radiosonde observation value. This feature should be valid also for comparison of IWV from sun photometer and other instruments. Maximum 10% error level of IWV from sun photometer observations, when compared with radiosondes, have been found for the Arctic. It is in the same order of magnitude than at tropical and middle latitudes locations. It has been demonstrated the feasibility of AERONET IWV observations in the Arctic for research on this variable. AERONET standard instruments and its centralized-standard processing algorithm allow its IWV observations to be considered a relative standard dataset for the re-calibration of other instrumental IWV observations assuming radiosondes as the absolute standard dataset. • Dry bias of integrated water vapor from sun photometers also present in the Arctic. • Integrated water vapor maximum 10% error between sun photometer and radiosondes • Sun photometers integrated water vapor suitable for other datasets re-calibration. [ABSTRACT FROM AUTHOR]

Atmospheric Boundary Layer (ABL) characteristics are investigated using a Ceilometer Lidar over Ahmedabad, a semi-arid region in western India. Strong diurnal variations of ABL are observed during 2019, the observation period. There is a stark winter-summer difference in ABL, with summer Boundary Layer Height (BLH) exceeding winter BLH by 1–1.5 km. ABL usually collapses during monsoon and is equivocal due to the presence of thick clouds on top of ABL. The ABL is thicker during the onset of monsoon in contrast to active monsoon, rises again during the withdrawal of monsoon. Lidar observed ABL has been compared with satellite, radiosonde, and European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) dataset. ERA5 shows good agreement with differences within 500 m; radiosonde observations have under-estimated ground-based measurements, especially during summer. Satellite observations highly overestimated BLH. This comparative study reveals the importance of ground-based lidars in continuous monitoring of ABL at high resolution because radiosonde, satellite, and reanalysis datasets have coarser resolutions and sparse observations. Such quantitative evaluation of ABL is formerly unavailable over this region, which can now be used to improve the representation in numerical models and thereby estimates of radiative and climate effects due to ABL. • Atmospheric Boundary Layer (ABL) characteristics have been studied using Ceilometer Lidar. • Strong diurnal variations have been observed; Day-to-day, monthly and seasonal variations are also prominent. • Summer-winter difference 1-1.5km; high during monsoon onset, meagre during active and rises again with break phase. • ERA-5 in good agreement with Ceilometer; Sonde and GPS RO retrievals are underestimated and overestimated, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A study is presented focusing on the potential value of parameters derived from radiosonde data or data from numerical atmospheric models for the forecasting of severe weather associated with convective storms. Parameters have been derived from soundings in the proximity of large hail, tornadoes (including tornadoes over water: waterspouts) and thunderstorms in the Netherlands. 66,365 radiosonde soundings from six stations in and around the Netherlands between 1 Dec. 1975 to 31 Aug. 2003 were classified as being associated or not associated with these weather phenomena using observational data from voluntary observers, the Dutch National Meteorological Institute (KNMI) and lightning data from the U.K. Met. Office. It was found that instability as measured by the Lifted Index or CAPE and 0–6 km wind shear independently have considerable skill in distinguishing environments of large hail and of non-hail-producing thunderstorms. It was also found that CAPE released below 3 km above ground level is on average high near waterspouts and weak tornadoes that mostly occur with low shear in the lowest 1 km above the Earth''s surface. On the other hand, low-level shear is strong in environments of stronger (F1 and F2) tornadoes and increases with increasing F-scale. This is consistent with the notion that stretching of pre-existing vertical vorticity is the most important mechanism for the formation of weak tornadoes while the tilting of vorticity is more important with stronger tornadoes. The presented results may assist forecasters to assess the likelihood of severe hail or tornadoes. [Copyright &y& Elsevier]

Abstract: The cloud vertical structure (CVS) of Arctic clouds is analyzed with data mainly from radiosondes launched between November 2003 and June 2004 during the Canadian Arctic Shelf Exchange Study (CASES). The feasibility of using a radiosonde-based cloud detection method [Minnis, P., Yi, Y. Huang, J., and Ayers, K. 2005: Relationships between radiosonde and RUC-2 meteorological conditions and cloud occurrence determined from ARM data, J. Geophys. Res., 110, D23204, doi:10.1029/2005JD006005. MN05 hereafter] is evaluated. At temperatures between −35 and 5 °C, the minimum probability (Pr) calculated from MN05 to detect a cloud layer is 68%. The infeasibility of MN05 in determining Arctic cirrus clouds is speculated to be due to the different freezing mechanisms at low temperatures (< −40 °C) in polluted continental and clean Arctic environments. Based on these facts we present a modified scheme to determine CVS in this paper. 1) for low clouds, 51.6% of all samples are with cloud base height (CBH)<500 m; 66.5% with cloud top height (CTH)<1500 m and 80.6% with CTH<2500 m; 54.7% with cloud vertical thickness (CVT)<500 m and 73.6% with CVT<1000 m; 2) for middle clouds, the CBH is almost evenly distributed between 1.8 and 4 km but 68% of all CTHs are at heights between 2000 and 5000 m. 17% of CTHs are above 8000 m and 47% CVTs are thinner than 1000 m and 67% thinner than 2000 m; 3) for high clouds, the frequency distributions of both CBH and CTH decrease with increasing height from 5000 to 8000 m but there are 41% CBHs between 9000 and 11,500 m. The MODIS-derived cloud top pressure (CTP) is compared with data from radiosondes. In general the MODIS CTP agrees well with that from radiosondes between the 400 and 700 hPa layer. MODIS underestimates CTP at heights between 700 and 950 hPa and overestimates CTP at lower layers (>950 hPa). The underestimate and overestimate of atmospheric temperatures above and under the 950 hPa isobaric layer respectively is thought to be the cause of the differences. [Copyright &y& Elsevier]

Abstract: Planetary boundary layer (PBL) and dust layer (DL) height evolution have systematically been investigated during the past 2 years at Lecce, Italy (40.33°N, 18.10°E) using a lidar. These heights are identified as the height at which the first and second measurable minima of the derivative of the lidar signal normalized to the backscatter molecular signal occurs. The PBL and DL heights were lower during the summer than the winter, contrary to what is expected. This behavior can be explained in terms of the suppression of the boundary layer depth growth caused by the advection of marine air. It is shown that PBL and DL heights retrieved by lidar are in good agreement with the ones obtained by radiosounding measurements from a close meteorological station. [Copyright &y& Elsevier]